Self-focusing laser Doppler vibration measurement method and system capable of resisting natural vibration of optical fiber

Abstract

The invention belongs to the technical field of laser vibration measurement, and provides a self-focusing laser Doppler vibration measurement method and system capable of resisting self-vibration of an optical fiber, and the method comprises the steps: adding a compensation light path which is used for sensing and generating reference light which is equal to an interference signal in amplitude and is opposite to the interference signal in real time in a Doppler vibration measurement light path, and taking the minimum mean square error as a self-adaptive matching criterion; interference phases obtained by synchronous demodulation of the compensation light path and the main light path are subjected to adaptive matching and cancellation in amplitude and phase dimensions, residual errors of vibration of the vibration measurement system and other environmental interferences are suppressed below noise of the vibration measurement system, and the purpose of balancing and weakening optical fiber vibration interferences in an instrument is achieved. The influence of the vibration factor of the instrument is reduced, and the interference influence is accurately eliminated through amplitude and phase matching by a demodulation algorithm corresponding to a compensation light path; meanwhile, by dynamically observing and updating the return light intensity threshold, low-frequency disturbance is resisted, and accurate automatic focusing is achieved.

Description

Technical Field

[0001] This invention belongs to the field of laser vibration measurement technology, and in particular relates to a self-focusing laser Doppler vibration measurement method and system that resists fiber optic self-vibration. Background Technology

[0002] All-fiber laser doppler vibrometers (AFLDVs), with their all-fiber optical path, absence of mechanical scanning components, high sensitivity, and ability to perform long-distance non-contact measurements, have been widely applied in high-precision scenarios such as online monitoring of aero-engine blades, dynamic testing of microelectromechanical systems (MEMS), wheel-rail contact vibration detection in rail transit, and on-orbit health monitoring of space structures. However, these applications are often accompanied by interference factors such as strong vibrations of the platform itself, rapid changes in ambient temperature / pressure, and signal attenuation caused by complex reflective surfaces.

[0003] In traditional AFLDV operation, the instrument is severely affected by external environmental vibrations, leading to artifacts from the instrument's internal optical path motion in the measurement signal. This results in false information in the demodulated vibration signal that does not reflect the true vibration state. Specifically, because the optical signal is completely confined within the optical fiber, any mechanical vibration of the fiber itself directly modulates the phase and frequency of the transmitted light. This modulation effect is particularly pronounced when the external vibration amplitude is large, manifesting as a parasitic frequency shift in the instrument's output spectrum that is on the same order of magnitude as the measured signal, severely reducing measurement accuracy. Current technologies for suppressing fiber self-vibration interference mainly rely on structural vibration isolation or post-processing filtering, which increases system size and cost without fundamentally eliminating the interference. In addition, existing focusing algorithms typically assume constant environmental optical parameters, making it difficult to maintain optimal focusing in complex and dynamically changing environments, thus reducing vibration measurement accuracy and reliability. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a self-focusing laser Doppler vibration measurement method and system with anti-fiber self-vibration capability. This invention adds a compensation optical path to the optical path, achieving the goal of balancing and weakening fiber vibration interference within the instrument and reducing the impact of the instrument's own vibration factors. The demodulation algorithm corresponding to the compensation optical path accurately eliminates interference through amplitude and phase matching. Simultaneously, by dynamically observing and updating the return light intensity threshold, it resists low-frequency disturbances and achieves precise automatic focusing. Through the compensation optical path, demodulation, and self-focusing, the stability and reliability of the all-fiber laser vibration meter in complex environments are significantly improved, enhancing its adaptability to harsh environments.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a self-focusing laser Doppler vibration measurement method to resist fiber optic self-oscillation. A compensation optical path is added inside the Doppler vibration measurement optical path for real-time sensing and generation of a reference light with the same amplitude but opposite phase to the interference signal. The method includes: The phase and amplitude of the main optical path and the compensation optical path are extracted. Using the minimum mean square error as the adaptive matching criterion, the interference phases obtained by synchronous demodulation of the compensation optical path and the main optical path are adaptively matched and canceled in the amplitude and phase dimensions, respectively, so as to suppress the residual error of the vibration of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. Real-time monitoring of backlight intensity changes, elimination of low-frequency oscillation interference, and dynamic observation and updating of backlight intensity thresholds to resist low-frequency disturbances and achieve automatic focusing.

[0006] Furthermore, the main optical path includes a laser, an attenuator connected to the laser, a first beam splitter connected to the attenuator, a second beam splitter and an acousto-optic modulator connected to the first beam splitter, a first circulator connected to the second beam splitter, a first coupler connected to the first circulator, a lens connected to the first coupler, a third beam splitter connected to the acousto-optic modulator, a third coupler connected to the third beam splitter, and a first photodetector connected to the third coupler; the first circulator is also connected to the third coupler; the compensation optical path includes a second circulator connected to the second beam splitter, a second coupler connected to the second circulator, a collimator connected to the second coupler, a fourth coupler connected to the third beam splitter, and a second photodetector connected to the fourth coupler; the second circulator is also connected to the fourth coupler.

[0007] Furthermore, the first circulator and the second coupler are of the same model and have the same specifications; all fiber segments of the compensation optical path are mechanically bonded to the corresponding fiber segments of the main optical path using the same path, the same sheath, and the same fixing method, so that the optical path disturbances experienced by the two paths are consistent.

[0008] Furthermore, during adaptive matching and cancellation, a phase generation carrier demodulation algorithm is used to demodulate the intermediate frequency current signals of the main optical path and the compensation optical path. The intermediate frequency current signals are multiplied by the sine carrier and the cosine carrier respectively to obtain the mixed signal. The combined signal is filtered out by a low-pass filter, and the difference frequency signal is retained to obtain two orthogonal signals.

[0009] Furthermore, for phase matching, an offset signal is selected. Interference signals in the main optical path The maximum cross-correlation between them determines the phase offset. Select the phase shift corresponding to the maximum cross-correlation. Phase alignment is performed to obtain the alignment signal. For amplitude matching, solve for the scaling factor. It satisfies the following formula: ; The objective function is: ; right Taking the derivative and setting it to 0, we get: ; The demodulation results of the main optical path are compensated using the demodulation results of the compensated optical path to obtain a demodulated signal free from its own vibration interference. : ; in The demodulated main optical path phase.

[0010] Furthermore, to resist low-frequency disturbances by dynamically observing and updating the backlight intensity threshold: a motor, a guide rail that can be driven by the motor, and a focusing lens on the guide rail are set between the probe light and the object under test; by controlling the movement of the focusing lens, the focal position of the optical antenna is changed so that the backlight power is highest when the focal point is on the surface of the object under test, corresponding to the maximum mid-frequency current amplitude, thus achieving automatic focusing.

[0011] Furthermore, the peak-to-peak values ​​of the photodetector output are continuously collected, and multiple samples are cached; the mean and standard deviation of the current samples are calculated, and the threshold interval is updated; if a preset number of consecutive samples in the cache are greater than the threshold interval, the current motor position is recorded; after the motor reaches the limit, the potential focal interval is obtained; the process of caching samples, updating the threshold interval, and recording the current motor position is repeated until the final focal position is obtained.

[0012] Secondly, the present invention also provides a self-focusing laser Doppler vibration measurement system to resist fiber optic self-oscillation. A compensation optical path is added inside the Doppler vibration measurement optical path for real-time sensing and generation of a reference light with the same amplitude but opposite phase to the interference signal. The system includes: The demodulation module is configured to: extract the phase and amplitude of the main optical path and the compensation optical path; and use the minimum mean square error as the adaptive matching criterion to adaptively match and cancel the interference phase obtained by synchronous demodulation of the compensation optical path and the main optical path in the amplitude and phase dimensions, respectively, so as to suppress the residual error of the vibration of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. The autofocus module is configured to: monitor the trend of backlight intensity changes in real time, eliminate low-frequency oscillation interference, and resist low-frequency disturbances by dynamically observing and updating the backlight intensity threshold to achieve autofocus.

[0013] Thirdly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in the first aspect.

[0014] Fourthly, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor, wherein the processor executes the program to implement the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in the first aspect.

[0015] Fifthly, the present invention also provides a computer program product, the computer program product comprising a computer program, which, when executed by a processor, implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in the first aspect.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention adds a compensation optical path inside the Doppler vibration measurement optical path to sense and generate a reference light with the same amplitude and opposite phase as the interference signal in real time. Using the minimum mean square error as the adaptive matching criterion, the interference phase obtained by synchronous demodulation of the compensation optical path and the main optical path is adaptively matched and canceled in both amplitude and phase dimensions, suppressing the residual error of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. The addition of the compensation optical path in the optical path achieves the purpose of balancing and weakening the fiber vibration interference in the instrument, reducing the influence of the instrument's own vibration factors. The demodulation algorithm corresponding to the compensation optical path accurately eliminates the interference effect through amplitude and phase matching. At the same time, by dynamically observing and updating the return light intensity threshold, it resists low-frequency disturbances and achieves accurate automatic focusing. Through the compensation optical path, demodulation, and self-focusing, the stability and reliability of the all-fiber laser vibration meter in complex environments are significantly improved, enhancing its adaptability to harsh environments. Attached Figure Description

[0017] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0018] Figure 1 This is the all-fiber laser Doppler vibratory optical path for resisting fiber optic self-oscillation interference in Embodiment 1 of the present invention; Figure 2 This is the self-focusing structure of the all-fiber laser Doppler vibrometer of Embodiment 1 of the present invention; Figure 3 This is a block diagram of the autofocus algorithm in Embodiment 1 of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] Example 1: In the field of laser vibration measurement, although traditional spatial optical path laser vibrometers have achieved vibration measurement at the micron and even nanometer level, they are significantly affected by mechanical vibration, temperature drift, and dust contamination in complex industrial environments, making it difficult to balance long-term stability and maintenance costs. In contrast, the all-fiber laser Doppler vibrometer (AFLDV) replaces the discrete spatial optical path with an all-fiber optical path, offering advantages such as high integration, compact structure, alignment-free operation, and easy maintenance, and has gradually become the preferred solution for on-site monitoring in complex working conditions.

[0022] However, precisely because the optical signal is completely confined within the optical fiber, any mechanical vibration of the fiber itself (whether it be platform jitter, acoustic coupling, or length-refractive index perturbation caused by temperature gradient) will directly modulate the phase and frequency of the transmitted light. When the amplitude of external vibration is large, this modulation effect is particularly prominent, manifesting as a parasitic frequency shift in the instrument's output spectrum that is on the same order of magnitude as the measured signal, severely reducing measurement accuracy.

[0023] Current technologies for suppressing fiber optic self-vibration interference mainly rely on structural vibration isolation or post-processing filtering, which increases system size and cost and cannot fundamentally eliminate the interference. Existing technologies lack novel optical path structures that actively cancel fiber vibration modulation from within the optical path, as well as matching demodulation algorithms.

[0024] On the other hand, the magnitude of the backlight power directly determines the signal-to-noise ratio of the measured signal. The highest backlight efficiency can be obtained by focusing the beam at the focal point; therefore, laser vibrometers generally use "maximum backlight power" as the autofocus criterion. During focusing, the amplitude of the intermediate frequency current is usually used as a real-time representation of the backlight power. However, due to low-frequency disturbances such as fluctuations in the spatial distribution of laser output intensity, electrical noise, fiber vibration, and environmental speckle, the amplitude of the intermediate frequency current is often accompanied by significant low-frequency oscillations. If only the peak position is used as the focusing basis, misjudgment is likely to occur, leading to inaccurate focusing.

[0025] To address at least one of the aforementioned problems, this embodiment provides a self-focusing laser Doppler vibration measurement method to combat fiber optic self-oscillation. Specifically, to meet the demands of complex industrial environments for high stability and reliability in laser vibration measurement, a novel optical path capable of actively suppressing fiber optic self-oscillation modulation is proposed, along with a demodulation algorithm that works in conjunction with this optical path to achieve precise cancellation of interference signals in the phase-amplitude dimension. Furthermore, an autofocusing algorithm resistant to low-frequency disturbances is proposed, eliminating the risk of misfocusing caused by low-frequency oscillations through a dynamic threshold and trend discrimination mechanism. These innovations significantly improve the adaptability and measurement accuracy of the all-fiber laser Doppler vibration meter in complex environments with strong vibration and noise.

[0026] Specifically, in the design of the compensation optical path, based on clarifying the interference formation mechanism of "fiber self-vibration → phase modulation → frequency shift artifacts", this embodiment adds a self-vibration compensation arm inside the optical path. This compensation arm (compensation optical path) shares the same vibration environment with the main measurement arm (main optical path), and can sense and generate reference light with the same amplitude and opposite phase as the interference signal in real time; for the first time, it achieves "observable" capability of instrument self-vibration and external disturbances at the hardware level, laying the foundation for subsequent accurate suppression. For the above-mentioned compensation optical path, the proposed matching demodulation algorithm is as follows: by synchronously extracting the phase and amplitude information of the main measurement arm and the compensation arm, a two-parameter error model is established, and adaptive matching is completed with the minimum mean square error as the criterion; this algorithm not only achieves high-fidelity vibration demodulation under the improved optical path conditions, but also suppresses the residual error of instrument self-vibration and other environmental interferences to below the system noise, significantly improving measurement accuracy and robustness. Focusing accuracy directly determines the backlight power and signal-to-noise ratio. This embodiment proposes a self-focusing algorithm based on dynamic threshold: it monitors the trend of backlight intensity changes in real time, eliminates low-frequency oscillation interference caused by speckle noise, electrical noise, etc., and only responds to the essential feature of "sharp increase in backlight intensity at the focal point". This algorithm can still reliably lock the focus in extreme scenarios such as low backlight and complex reflective surfaces, further ensuring the stable operation of the instrument in changing environments.

[0027] The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration in this embodiment designs a fiber optic self-vibration compensation optical path to balance the vibration modulation signal generated by the fiber optic cable due to environmental influences, thereby improving the accuracy and robustness of the instrument's demodulation results. A demodulation algorithm based on the anti-fiber optic self-vibration optical path is designed, achieving precise location and elimination of interference signals through phase matching and amplitude matching. Furthermore, a local variance weighted adaptive dynamic threshold method is established to process intermediate frequency current peak signals, capture rapid light intensity fluctuations, and resist low-frequency interference generated by laser speckle noise and environmental noise. The specific implementation process includes: S1. Anti-fiber self-oscillation all-fiber laser Doppler vibration measurement system: S1.1 Mechanism of optical fiber self-oscillation interference: The internal optical path of an all-fiber laser Doppler vibrometer relies on optical fiber connections. This means that mechanical vibration within the fiber itself will directly cause instantaneous changes in the fiber length L and its effective refractive index n, thereby modulating the phase of the laser propagating within it, manifesting as an instantaneous shift in the laser frequency. Assuming that vibration interference on the fiber causes changes in the equivalent optical path... for: (1) in, To reduce the amplitude of vibrations that interfere with changes in optical path length; This is the vibration frequency corresponding to the change in optical path length; For time. Introduced phase change of the reflected laser. for: (2) in, To detect the laser wavelength, Let be the refractive index of the optical fiber; and let the vibration displacement of the object being measured at this time be: (3) in, The amplitude of the vibration of the object being measured; The vibration frequency of the object being measured. The phase change of the reflected laser light is introduced. for: (4) Combining both, the phase of the interfering optical signal is: (5) Traditional phase demodulation algorithms can be used to extract the modulation phase from the intermediate frequency current signal output by a balanced photodetector. Finally, the vibration displacement was demodulated. As shown below: (6) Clearly, the demodulation result introduces interference signals caused by fiber vibration. : (7) S1.2, Implementation method of anti-fiber self-oscillation compensation optical path: S1.2.1 Overall Architecture: like Figure 1 As shown, the optical route consists of a 1550 nm narrow linewidth laser, a 635 nm indicator optical module, an optical fiber attenuator, a 1-to-2 optical fiber coupler, a polarization maintaining circulator, an acousto-optic modulator (AOM), a 2-to-2 optical fiber coupler, a reflector, and two balanced photodetectors.

[0028] The blue detection optical path (main optical path) is used to acquire the vibration signal of the target being measured. Optionally, the main optical path includes a laser, an attenuator connected to the laser, a first beam splitter connected to the attenuator, a second beam splitter and an acousto-optic modulator connected to the first beam splitter, a first circulator connected to the second beam splitter, a first coupler connected to the first circulator, a lens and an indicator light connected to the first coupler, a third beam splitter connected to the acousto-optic modulator, a third coupler connected to the third beam splitter, and a first photodetector connected to the third coupler; the first circulator is also connected to the third coupler.

[0029] The red compensation optical path (compensation optical path) is used to independently extract interference signals introduced by the vibration of the optical fiber itself; optionally, the compensation optical path includes a second circulator connected to the second beam splitter, a second coupler connected to the second circulator, a collimator connected to the second coupler, a fourth coupler connected to the third beam splitter, and a second photodetector connected to the fourth coupler; the second circulator is also connected to the fourth coupler.

[0030] S1.2.2, Detection optical path workflow: After the 1550 nm laser is reduced to a power safe for the human eye by an optical fiber attenuator, it first enters a 90:10 optical fiber beam splitter and is divided into measurement light (90%) and reference light (10%).

[0031] The measurement light is split again by a 90:10 ratio to generate a measurement optical path probe light (90%, which is subsequently used for target measurement) and a compensation optical path probe light (10%, which is injected into the compensation arm).

[0032] The measurement optical path probe light exits from port 1 to port 2 of the polarization-maintaining circulator (first circulator) and enters the 95:5 coupler (first coupler); 95% of the light is combined with the 635nm indicator light and then focused onto the surface of the object under test by the optical antenna.

[0033] The 1550nm echo reflected by the object is received by the optical antenna, and then enters the 50:50 coupler (third coupler) through port 2 to port 3 of the circulator (first circulator).

[0034] After the reference light is frequency-shifted by the AOM, it is split into a probe reference light and a compensation reference light by a 50:50 beam splitter (third beam splitter). The probe reference light enters the aforementioned 50:50 coupler (fourth coupler) and interferes with the echo light.

[0035] The interference signal is fed into a balanced photodetector, which outputs an intermediate frequency current. After demodulation by the control board, a composite signal containing the target vibration and fiber optic self-vibration components is obtained.

[0036] S1.2.3 Compensation Optical Path Workflow The compensation optical path probe light (10% measurement light) passes through a circulator (second circulator) of the same type as the probe optical path and a coupler of the same specification (second coupler), then illuminates a reflector rigidly fixed to the instrument and returns completely along the original path.

[0037] After the reflected light passes through port 2 to port 3 of the circulator, it interferes with the compensation reference light in the 50:50 coupler (the fourth coupler).

[0038] The interference signal is fed into the compensated optical path balanced photodetector, and the output intermediate frequency current is generated. .

[0039] To ensure equivalent sensing of fiber vibration in the detection optical path by the compensation optical path, all fiber segments of the compensation optical path and their corresponding fiber segments in the detection optical path are mechanically bonded using the same path, sheath, and fixing method, ensuring that the optical path disturbances experienced by both paths are completely identical. The intermediate frequency current output by the two balanced photodetectors is expressed as: (8) (9) in, To detect the output of the optical path; To compensate for the optical path output; The coefficient is constant. To detect the power of the optical path return signal; To detect the reference optical power of the optical path; Contains the vibration information of the object (frequency is ,in (The vibration frequency of the object being measured). Phase interference caused by fiber optic vibration; The initial random phase of the laser; This represents the phase difference between the measured light and the reference light. Subsequent algorithms utilize phase-amplitude matching of the two intermediate frequency currents to accurately eliminate [the affected light]. This enables hardware-level suppression of instrument self-oscillation interference.

[0040] S2. Phase amplitude matching demodulation algorithm based on anti-self-oscillating optical path: Based on the aforementioned all-fiber laser Doppler vibration measurement optical path designed to resist instrument self-oscillation, a demodulation algorithm is designed to demodulate the two intermediate frequency (IF) current signals. First, a phase-generated carrier (PGC) demodulation algorithm is used to demodulate the IF current signals from the two optical paths. This is achieved by... The resulting signal is obtained by multiplying the signal by a sine carrier and a cosine carrier, respectively, and then a low-pass filter is used to filter out the combined signal. Preserve the difference frequency signal Two orthogonal signals are obtained (taking demodulation of the probe optical path signal as an example): (10) The modulation phase is obtained using the arctangent algorithm: (11) neglect The effect can be used to obtain the demodulated vibration displacement: (12) Similarly, the phases demodulated by the PGC algorithm for the probe optical path and the compensation optical path can be obtained as follows: (13) From formula (13), we can see that Includes actual vibration displacement Interference with fiber optic vibration ,and Optical fiber vibration signal Measurements were performed, but due to differences in environment and devices, etc. and They are not completely equal; they do not match in amplitude or phase. This invention proposes the following method to achieve this. and Amplitude and phase matching: For phase matching, calculate and select the offset signal. Interference signals in the measurement optical path (main optical path) The maximum cross-correlation between them determines the phase offset. The cross-correlation is defined as follows: (14) Select Phase offset corresponding to the maximum right The signal is phase aligned to obtain the aligned signal. .

[0041] For amplitude matching, since and The amplitudes are not equal, so direct use reduce It will still exist The error of the feature necessitates a solution scaling factor. Make That is, to search Satisfy the following formula: (15) Let the objective function be: (16) right Taking the derivative and setting it to 0, we get: (17) The final demodulation result using the compensated optical path Demodulation results of the detection optical path Compensation is performed to obtain a demodulated signal that eliminates interference from the instrument's own vibration. : (18) The optical path and demodulation post-processing algorithm described above remove the instrument's own vibration interference by utilizing the demodulation results of the compensated optical path, which greatly improves the anti-interference capability of the all-fiber laser Doppler vibration meter and is expected to realize precise vibration measurement in complex environments.

[0042] S3. Environmental interference suppression based on dynamic threshold self-focusing algorithm: S3.1 System Composition: like Figure 2 As shown, the autofocus module consists of an all-fiber laser Doppler vibration measurement optical path, a stepper motor, and a control board. The control board reads the peak-to-peak value of the intermediate frequency current output by the balanced photodetector in real time (Equation (8)) and uses it as the feedback quantity of the return light power. By driving the stepper motor to move the focusing lens on the guide rail, the focal position of the optical antenna is changed. When the focal point is exactly located on the surface of the object being measured, the return light power is the highest, corresponding to the maximum intermediate frequency current amplitude, thereby realizing autofocus.

[0043] S3.2 Environmental Interference Mechanism: In actual working conditions, both the slight movement of the surface of the object being measured and the random spatial distribution of the emitted light intensity (speckle noise) will cause fluctuations in the echo intensity. Experiments show that even when the object is stationary, the echo intensity still exhibits random fluctuations, and the amplitude of these fluctuations varies. With the current maximum light intensity satisfy: (19) Among them, the proportionality coefficient It increases as the backlight weakens, and in extreme cases... ≈0.9. At this point, it is difficult to determine whether the current fluctuation originates from speckle noise or has actually reached the focal point based solely on the instantaneous amplitude. Therefore, a focusing strategy that resists low-frequency disturbances must be introduced.

[0044] S3.3, Dynamic Threshold Self-Focusing Algorithm The algorithm flow is as follows Figure 3 As shown, the steps are as follows: Initialization: The control board first resets the motor to zero; then the motor moves at a constant speed toward the limit end.

[0045] Real-time sampling: Continuously acquire the peak-to-peak value of the output of the balanced photodetector during the motion process, and buffer it. One sample ( Select according to needs, sufficient to reflect signal characteristics.

[0046] Dynamic threshold calculation: Calculate the mean of the current samples when the cache is full. with standard deviation Update threshold range As shown below: (20) in, This is the sensitivity factor. After calculation, clear the cache and reload with new samples.

[0047] Significant peak detection: If the buffer is continuous All samples are greater than If the position is considered to be the focal point, then the current motor position is recorded. .

[0048] Potential focal zone generation: After the motor reaches the limit, the potential focal zone is obtained. .

[0049] Fine scanning: The motor performs real-time sampling and significant peak detection again within the above-mentioned range, dynamically updating the threshold and the current motor position. Continue until the final focus position is obtained.

[0050] Complete focus: Control the motor movement to the final position. This enables precise focusing.

[0051] The algorithm has a space and time complexity of O(N). This can be improved by flexibly adjusting the parameters. , , It can effectively suppress low-frequency fluctuations in the amplitude of intermediate frequency current while ensuring real-time performance, enabling fast, stable, and accurate automatic focusing in complex environments.

[0052] In summary, this embodiment systematically analyzes the physical mechanism of phase-frequency modulation caused by the instrument's own vibration in the optical fiber, and adds a compensation optical path to the traditional all-fiber Doppler vibration measurement optical path. This compensation optical path is isomorphic, has the same path length, and is mechanically bound to the main measurement optical path. It can sense the equivalent optical path disturbance caused by the vibration of the optical fiber itself in real time and independently, thereby directly obtaining the observation channel of "instrument self-vibration" at the hardware level, which significantly improves the anti-interference capability compared with the traditional optical path.

[0053] Based on the PGC demodulation framework, this embodiment proposes an amplitude-phase matching algorithm that works in conjunction with the aforementioned compensation optical path: the interference phases obtained by synchronous demodulation of the compensation optical path and the main optical path are adaptively matched and canceled in the amplitude and phase dimensions, respectively; this algorithm does not require an additional reference sensor and can suppress the contribution of environmental disturbances to the demodulation results to below the system noise, ensuring the accuracy of target vibration extraction.

[0054] Based on the real-time statistical characteristics of mid-frequency current amplitude, this embodiment develops a dynamic threshold self-focusing algorithm: during motion scanning, the local mean and standard deviation are continuously calculated to quickly identify significant jumps in backlight intensity using an adaptive threshold, and the focus is locked through a secondary fine scan. The algorithm has a space-time complexity of O(N), which can be directly embedded in lower-level machines such as FPGAs or DSPs to achieve millisecond-level real-time focusing, while effectively suppressing speckle noise and other low-frequency interference.

[0055] Example 2: This embodiment provides a self-focusing laser Doppler vibration measurement system to resist fiber optic self-oscillation. A compensation optical path is added inside the Doppler vibration measurement optical path for real-time sensing and generation of a reference light with the same amplitude but opposite phase to the interference signal. The system includes: The demodulation module is configured to: extract the phase and amplitude of the main optical path and the compensation optical path; and use the minimum mean square error as the adaptive matching criterion to adaptively match and cancel the interference phase obtained by synchronous demodulation of the compensation optical path and the main optical path in the amplitude and phase dimensions, respectively, so as to suppress the residual error of the vibration of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. The autofocus module is configured to: monitor the trend of backlight intensity changes in real time, eliminate low-frequency oscillation interference, and resist low-frequency disturbances by dynamically observing and updating the backlight intensity threshold to achieve autofocus.

[0056] The working method of the system is the same as that of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration in Example 1, and will not be repeated here.

[0057] Example 3: This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in Embodiment 1.

[0058] Example 4: This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the program, it implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration described in Embodiment 1.

[0059] Example 5: This embodiment provides a computer program product, which includes a computer program. When the computer program is executed by a processor, it implements the steps of the self-focusing laser Doppler vibration measurement method against fiber optic self-vibration described in Embodiment 1.

[0060] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A self-focusing laser Doppler vibration measurement method for resisting fiber optic self-oscillation, characterized in that, A compensation optical path is added inside the Doppler vibration measurement optical path for real-time sensing and generation of a reference light with the same amplitude but opposite phase to the interference signal. The method includes: The phase and amplitude of the main optical path and the compensation optical path are extracted. Using the minimum mean square error as the adaptive matching criterion, the interference phases obtained by synchronous demodulation of the compensation optical path and the main optical path are adaptively matched and canceled in the amplitude and phase dimensions, respectively, so as to suppress the residual error of the vibration of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. Real-time monitoring of backlight intensity changes, elimination of low-frequency oscillation interference, and dynamic observation and updating of backlight intensity thresholds to resist low-frequency disturbances and achieve automatic focusing.

2. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 1, characterized in that, The main optical path includes a laser, an attenuator connected to the laser, a first beam splitter connected to the attenuator, a second beam splitter and an acousto-optic modulator connected to the first beam splitter, a first circulator connected to the second beam splitter, a first coupler connected to the first circulator, a lens connected to the first coupler, a third beam splitter connected to the acousto-optic modulator, a third coupler connected to the third beam splitter, and a first photodetector connected to the third coupler; the first circulator is also connected to the third coupler; the compensation optical path includes a second circulator connected to the second beam splitter, a second coupler connected to the second circulator, a collimator connected to the second coupler, a fourth coupler connected to the third beam splitter, and a second photodetector connected to the fourth coupler; the second circulator is also connected to the fourth coupler.

3. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 2, characterized in that, The first circulator and the second coupler are of the same model and have the same specifications; all fiber segments of the compensation optical path are mechanically bonded to the corresponding fiber segments of the main optical path using the same path, the same sheath, and the same fixing method, and the optical path disturbances experienced by the two paths are consistent.

4. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 2, characterized in that, When performing adaptive matching and cancellation, the phase generation carrier demodulation algorithm is used to demodulate the intermediate frequency current signals of the main optical path and the compensation optical path. The intermediate frequency current signals are multiplied by the sine carrier and the cosine carrier respectively to obtain the mixed signal. The combined signal is filtered out by a low-pass filter, and the difference frequency signal is retained to obtain two orthogonal signals.

5. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 4, characterized in that, For phase matching, select the offset signal. Interference signals in the main optical path The maximum cross-correlation between them determines the phase offset. ; Select the phase shift corresponding to the maximum cross-correlation. Phase alignment is performed to obtain the alignment signal. For amplitude matching, solve for the scaling factor. It satisfies the following formula: ； The objective function is: ； right Taking the derivative and setting it to 0, we get: ； The demodulation results of the main optical path are compensated using the demodulation results of the compensated optical path to obtain a demodulated signal free from its own vibration interference. : ； in The demodulated main optical path phase.

6. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 1, characterized in that, To resist low-frequency disturbances by dynamically observing and updating the backlight intensity threshold: a motor, a guide rail that can be driven by the motor, and a focusing lens on the guide rail are set between the probe light and the object under test; by controlling the movement of the focusing lens, the focal position of the optical antenna is changed so that the backlight power is highest when the focal point is on the surface of the object under test, corresponding to the maximum intermediate frequency current amplitude, thus achieving automatic focusing.

7. The self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in claim 6, characterized in that, The peak-to-peak value of the photodetector output is continuously collected and multiple samples are buffered; the mean and standard deviation of the current samples are calculated and the threshold interval is updated; if a preset number of samples in the buffer are all greater than the threshold interval, the current motor position is recorded; after the motor reaches the limit, the potential focal interval is obtained. Repeat the process of caching samples, updating the threshold range, and recording the current motor position until the final focus position is obtained.

8. A self-focusing laser Doppler vibration measurement system resistant to fiber optic self-oscillation, characterized in that, A compensation optical path is added inside the Doppler vibration measurement optical path for real-time sensing and generation of reference light with the same amplitude but opposite phase to the interference signal. The system includes: The demodulation module is configured to: extract the phase and amplitude of the main optical path and the compensation optical path; and use the minimum mean square error as the adaptive matching criterion to adaptively match and cancel the interference phase obtained by synchronous demodulation of the compensation optical path and the main optical path in the amplitude and phase dimensions, respectively, so as to suppress the residual error of the vibration of the vibration measurement system itself and other environmental interferences to below the noise of the vibration measurement system. The autofocus module is configured to: monitor the trend of backlight intensity changes in real time, eliminate low-frequency oscillation interference, and resist low-frequency disturbances by dynamically observing and updating the backlight intensity threshold to achieve autofocus.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, When the processor executes the program, it implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in any one of claims 1-6.

10. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the steps of the self-focusing laser Doppler vibration measurement method for resisting fiber optic self-vibration as described in any one of claims 1-6.

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